The field of the invention is a reception and detection solution in a radio system. More particularly the invention relates to the observation of co-channel interferences in a receiver.
In a cellular radio system, the quality of the connection between a base transceiver station and a subscriber terminal varies all the time. This variation is caused by radio waves that are fading as a function of distance and time in a fading channel and by interfering factors on the radio path, such as other signals on the same channel. In the cellular radio system, the same frequency must be continually used in different cells because of the limited scope of the frequency range. Co-channel signals usually coming from various transmitters arrive at a receiver operating at a certain frequency, which co-channel signals have propagated along various paths and which are thus multipath signals. The performance of a receiver can be improved by using joint detection of the most strongest interferences.
If co-channel detection is used in a situation or environment, in which co-channel interference does not occur, but the interference is mainly noise, the performance of a receiver weakens. This is due to the fact that the receiver uses estimated channel taps of the co-channel without co-channel interference, which increases noise e.g. in the transition metrics of the trellis in a Viterbi detector, and the probability of a bit error of the detector increases. As the environment and situation of a mobile terminal in particular change all the time, the terminal is sometimes in a situation with co-channel interference, whereas at other times the greatest interference is noise.
The object of the invention is thus to provide a method and a receiver implementing the method in such a manner that the above problems can be solved. The invention relates to a reception method used in a radio system, in which a receiver receives signals comprising a desired signal and one or more interference signals, which desired signal and interference signals comprise a predetermined sequence, by which the signals can be separated from each other. Further in the inventive method, a signal estimate of the desired signal is formed by means of the predetermined sequence of the desired signal; the most interfering interference signal is searched and a co-channel signal estimate is formed by means of the predetermined sequences of the desired signal and the interference signal; the first residual signal is formed, which describes the difference between the received signal and the signal estimate of the desired signal; the second residual signal is formed, which describes the difference between the received signal and co-channel signal estimate; the first residual signal is compared with the second residual signal and on the basis of the comparison, the received signal is detected either by one signal detection, whereby the effect of the interference signal on the desired signal is left unnoticed, or by joint detection, whereby the effect of the interference signal on the detection of the desired signal is taken into account.
The invention also relates to a receiver for a radio system, in which signals to be received comprise a desired signal and one or more at least occasionally occurring interference signals, which desired signal and interference signal comprise a predetermined sequence, by which the signals can be separated from each other. The receiver of the invention is characterized in that the receiver comprises: means for searching for the most interfering interference signal; means for forming a signal estimate of the desired signal by means of the predetermined sequence of the desired signal; means for forming a co-channel signal estimate by means of the predetermined sequences of the desired signal and interference signal; means for forming the first residual signal, which describes the difference between the received signal and the signal estimate of the desired signal; means for forming the second residual signal, which describes the difference between the received signal and co-channel signal estimate; means for comparing the first residual signal with the second residual signal and for selecting for a detector on the basis of the comparison either a one signal detection or joint detection to detect the received signal.
The preferred embodiments of the invention are disclosed in the dependent claims.
The method and system of the invention provide a plurality of advantages. The detection of a received signal improves, as the detection is suitably optimised both in the situations in which co-channel interferences occur or do not occur.